The floating balls sign refers to the appearance of multiple mobile globules/spherules of solid, usually fatty, tissue within an adnexal cyst. It is pathognomonic for ovarian mature cystic teratoma 1,2.
Alternative names include the meatballs 3 or truffle sign 4.
When a single large ball is floating at a fat-fluid interface, the name Pokemon (Poké) ball sign has been used 1.
The term sack of marbles sign has also been applied to this appearance but it is more commonly used to describe dermoid cysts of the head and neck 11,12.
Though thought to be uncommon, the sensitivity is up to 25% in some case series 1.
The balls represent spherules of sebaceous or keratinoid debris 1-3. They are different from Rokitansky nodules, which are nonfloating mural protuberances 9. The balls float due to their lower specific gravity compared to cyst fluid 10.
The balls are discrete spherical structures located within a cystic mass. They range in size, even within the same cyst, from 5 mm to 4 cm diameter 2. They also range in number, sometimes in excess of 100 within one cyst 2.
Two-thirds contain fat demonstrable by CT or MRI 1.
The balls are echogenic on a background of anechoic/hypoechoic fluid 1-7. No color Doppler signal is present within.
The balls vary in density, from fat density to soft tissue density (-70 to +35 HU) 1. Sometimes the balls have a fluid or soft tissue density core surrounded by a fat density rim 3.
The signal characteristics of the balls usually reflect the sebaceous composition 5,6.
- T1: hyperintense rim compared to surrounding fluid, relatively hypointense center
- T2: hypointense rim compared to the surrounding fluid, relatively hyperintense center compared to the outer portion
Fat-saturated sequences or an out-of-phase T1-weighted gradient-echo sequence may demonstrate signal drop, but this is not always present 8.
- 1. Şahin H, Akdoğan AI, Ayaz D, Karadeniz T, Sancı M. Utility of the "floating ball sign" in diagnosis of ovarian cystic teratoma. (2019) Turkish journal of obstetrics and gynecology. 16 (2): 118-123. doi:10.4274/tjod.galenos.2019.67209 - Pubmed
- 2. Tongsong T, Wanapirak C, Khunamornpong S, Sukpan K. Numerous intracystic floating balls as a sonographic feature of benign cystic teratoma: report of 5 cases. (2006) Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 25 (12): 1587-91. doi:10.7863/jum.2006.25.12.1587 - Pubmed
- 3. Mahomedy S, Bayat MR, Seedat M. Meat balls: a pathognomonic ultrasound and computed tomography finding in mature cystic teratoma. (2007) Australasian radiology. 51 Suppl: B281-3. doi:10.1111/j.1440-1673.2007.01807.x - Pubmed
- 4. Otigbah C, Thompson MO, Lowe DG, Setchell M. Mobile globules in benign cystic teratoma of the ovary. (2000) BJOG : an international journal of obstetrics and gynaecology. 107 (1): 135-8. doi:10.1111/j.1471-0528.2000.tb11592.x - Pubmed
- 5. Kawamoto S, Sato K, Matsumoto H, Togo Y, Ueda Y, Tanaka J, Heshiki A. Multiple mobile spherules in mature cystic teratoma of the ovary. (2001) AJR. American journal of roentgenology. 176 (6): 1455-7. doi:10.2214/ajr.176.6.1761455 - Pubmed
- 6. Umesaki N, Nagamatsu A, Yada C, Tanaka T. MR and ultrasound imaging of floating globules in mature ovarian cystic teratoma. (2004) Gynecologic and obstetric investigation. 58 (3): 130-2. doi:10.1159/000078952 - Pubmed
- 7. Jantarasaengaram S, Siricharoenthai S, Vairojanavong K. Cystic ovarian teratoma with intracystic fat balls. (2003) Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 22 (1): 102-3. doi:10.1002/uog.181 - Pubmed
- 8. Espindola APBP, Amorim VB, Koch HA, Bahia PRV, Almeida MVP. Atypical presentation of mature cystic teratoma ("floating balls"). (2017) Radiologia brasileira. 50 (3): 206-207. doi:10.1590/0100-3984.2015.0155 - Pubmed
- 9. Donnadieu AC, Deffieux X, Le Ray C, Mordefroid M, Frydman R, Fernandez H. Unusual fast-growing ovarian cystic teratoma during pregnancy presenting with intracystic fat "floating balls" appearance. (2006) Fertility and sterility. 86 (6): 1758-9. doi:10.1016/j.fertnstert.2006.06.016 - Pubmed
- 10. Tandon A, Agarwal R, Tandon R, Prakash M. Multiple intracystic floating balls: an unusual but unique sonographic pattern of mature cystic teratoma. (2011) BMJ case reports. doi:10.1136/bcr.03.2011.3962 - Pubmed
- 11. Wang A, Shu Y. Mature ovarian cystic teratoma with "sack of marbles" appearance on magnetic resonance imaging: A case report. (2019) Medicine. 98 (31): e16691. doi:10.1097/MD.0000000000016691 - Pubmed
- 12. Lee KH. 'Sack of marbles' in mature cystic ovarian teratoma. (2017) Abdominal radiology (New York). 42 (5): 1616-1617. doi:10.1007/s00261-017-1059-x - Pubmed